The present invention relates to image recording materials. More particularly the present invention provides a protective overcoat which provides excellent scratch and spill resistance to image recording materials.
Gelatin has been used extensively in a variety of image recording systems as the binder for its many unique properties. For example, its water-swellable property allows processing chemistry to be carried out to form silver halide-based photographic images, and its hydrophilic nature allows gelatin to function as an ink-receiver in ink-jet printing systems. However, due to this same property, recorded images, no matter if they are formed on transparent or reflective media, have to be handled with extreme care so as to not be in contact with any aqueous solutions to damage the images.
There have been attempts over the years to provide protective layers for gelatin-based photographic systems that will protect the images from damage by water or any aqueous solution. For example, U.S. Pat. No. 2,173,480 describes a method of applying a colloidal suspension to moist film as the last step of photographic processing before drying. A series of patents describe the methods of solvent-coating a protective layer on the image after photographic processing was completed. See, for example, U.S. Pat. Nos. 2,259,009, 2,331,746, 2,798,004, 3,113,867, 3,190,197, 3,415,670 and 3,733,293. There is also teaching describing the application of UV-polymerizable monomers and oligomers on processed images followed by radiation exposure to form a crosslinked protective layer. Radiation curable layers are exemplified in U.S. Pat. Nos. 4,092,173, 4,171,979, 4,333,998, and 4,426,431.
The obvious drawback for the solvent coating method and radiation cure method is the health and environmental concern of those chemicals to the coating operator. U.S. Pat. Nos. 3,397,980, 3,697,277 and 4,999,266 describe the method of laminating polymeric sheet film on the processed image as the protective layer. U.S. Pat. No. 5,447,832 describes the use of a protective layer containing a mixture of high and low Tg latices as the water-resistant layer to preserve the anti-static property of the V2O5 layer through photographic processing. This protective layer is not applicable to the image formation layers since it will detrimentally inhibit the photographic processing. U.S. Pat. No. 2,706,686 describes the use of a lacquer layer containing inorganic compound NH4HCO3 particles in the overcoat, followed by sublimation or dissolving of such compound in photographic processing and heat fusing to obtain a water resistant layer. However, the lacquer overcoat was applied as a suspension in an organic solvent and the volatiles or salts released from NH4HCO3 were major disadvantages in manufacturing as well as to photoprocessing laboratories. In addition, there are many patents disclosing overcoat formulations to improve scratch resistance of dry gelatin coatings, such as U.S. Pat. No. 5,179,147 among many others. However these overcoat formulations do not impart water resistance.
In general, all methods of protection requiring the application or coating of a layer after image formation suffer from the drawbacks of additional cost, the need for modifications to the processing equipment and additional operator training.
U.S. Pat. No. 5,853,926 describes the application of an aqueous coating comprising polymer particles in a polymer latex binder, allowing for development of a photographic image and after processing, fusing by heat to form a protective surface. The disadvantages of such a method include the limited photographic processing rates achievable when a polymer latex binder is used in the protective layer.
European Patent Application 0,858,905A1 describes a porous, particulate outermost layer applied to ink-jet recording media, that is heat-fused after ink absorption to form a protective surface. Such porous surface layers are often mechanically weak and in particular can be prone to scratching damage or material removal during transport and handling prior to image formation and subsequent fusing, thus compromising the usefulness of their protective function.
U.S. Pat. No. 5,856,051 describes the use of hydrophobic particles with gelatin as the binder in the overcoat formulation. This invention demonstrated an aqueous coatable, water-resistant protective overcoat that can be incorporated into the photographic product, allows for appropriate diffusion of photographic processing solutions, and does not require a coating operation after exposure and processing. The hydrophobic polymers exemplified in U.S. Pat. No. 5,856,051 include polyethylenes having a melting temperature (Tm) of 55 to 200xc2x0 C., and therefore capable of forming a water-resistant layer by fusing the layer at a temperature higher than the Tm of the polymer after the sample has been processed to generate the image. The coating solution is aqueous and can be incorporated in the manufacturing coating operation without any equipment modification. The fusing step is simple and environmentally friendly to photofinishing laboratories. Since the particles are incorporated entirely within the uppermost layer, this approach does not suffer from a lack of mechanical strength and integrity during transport and handling prior to image formation and fusing. However, the scratch resistance of such an overcoat after fusing is a serious concern, since polyethylene is a very soft material.
Thus, there remains a need for an aqueous coatable, water-resistant protective overcoat that can be incorporated into the image recording material during manufacturing, that is not damaged during machine transport and handling, that allows for appropriate diffusion of photographic processing solutions or uptake of ink, that does not require a coating operation after exposure and processing and that offers good scratch resistance.
The present invention provides an aqueous-coatable protective overcoat that can be coated on to the image recording material (either sequentially or simultaneously), allows for appropriate diffusion of photographic processing solutions or uptake of ink, and can be fused after photographic processing or ink-jet printing to form a water-resistant protective overcoat with good scratch resistance.
The present invention describes an uppermost-layer or overcoat composition that can be incorporated and coated directly in the image recording material during manufacturing, that does not inhibit photographic processing or uptake of ink, and that can become water-resistant by fusing the layer after it goes through photographic processing or ink-jet printing. A component of the invention is the hydrophobic polymer particles of polystyrene-type homo- or co-polymers consisting of at least 30% styrene-type monomers. The polymer can be either liner, graft or hyperbranched. The material of the invention can be introduced to the overcoat coating melt in a latex form or as a conventional colloidal dispersion in gelatin. When used at 50-70% by weight, based on total laydown of the overcoat where gelatin is the binder, it allows photographic processing to proceed at an acceptable rate. After processing to obtain images, the image recording media can be fused at a temperature above 300xc2x0 F. to form a water-resistant surface. Compared to U.S. Pat. No. 5,856,051 which describes the use of commercially available polyethylene particles, the polystyrene particles of the present invention offer improved dry scratch resistance.
Hence, the present invention provides:
An overcoat composition for image recording elements comprising:
30 to 95 weight percent, based on the dry laydown of the overcoat, of hydrophobic polymer particles having an average size of 0.01 to 0.5 micrometers, said hydrophobic polymer being a homopolymer of the monomer described in Structure 1 or a copolymer containing at least 30 weight percent, based on the total weight of monomers, of the monomer described in Structure 1 and 5 to 70 weight percent of gelatin, based on the dry laydown of the overcoat: 
wherein:
R is H, CH3, C2H5, and C3H7; and
X1, X2, X3, X4 and X5 are H, F, Cl, Br, I, CN, CH3O, C2H5O, C3H7O, C4H9O, CH3, C2H5, C3H7, n-C4H9, sec-C4H9, tert-C4H9, CF3, C2F5, C3F7, iso-C3F7, n-C4F9, sec-C4F9, tert-C4F9, CH3NH, (CH3)2N, n-C5H11, C4H9, n-C6H13, n-C7H15, n-C8H17, n-C9H19, n-C10H21, or n-C12H25.
Another aspect of the invention provides:
An imaging element comprising:
a support;
at least one image recording layer; and
an outer layer overlying the at least one image recording layer, the outer layer comprising the composition described above.
The present invention provides a novel overcoat formulation for the image recording side of image recording materials, particularly photographic prints, which encounter frequent handling and abuse by end users. The overcoat formulation of this invention comprises 30 to 95% by weight (based on the dry laydown of the overcoat) of hydrophobic polymer particles of 0.01 to 0.5 micrometers in average size and 5 to 70% by weight (based on the dry laydown of the overcoat) of gelatin as binder. Other common addenda, such as hardeners, spreading agents, charge control agents, dry scratch resistance compounds and lubricants can also be included in the formulation as needed. The hydrophobic polymer of this invention are homopolymers or copolymers containing at least 30% by weight of monomer described in Structure (1). 
wherein:
R is H, CH3, C2H5, or C3H7; and
X1, X2, X3, X4 and X5 are H, F, Cl, Br, I, CN, CH3O, C2H5O, C3H7O, C4H9O, CH3, C2H5, C3H7, n-C4H9, sec-C4H9, tert-C4H9, CF3, C2F5, C3F7, iso-C3F7, n-C4F9, sec-C4F9, tert-C4F9, CH3NH, (CH3)2N, n-C5H11, C4H9, n-C6H13, n-C7H15, n-C8H17, n-C9H19, n-C10H21, or n-C12H25.
The polymer architecture can be linear, block, dendritic, hyperbranched or grafted. The comonomers that can be included in the polymer composition are ethylene, propylene, 1-butene, sodium vinylbenzenesulfonate, potassium vinylbenzylsulfonate, sodium vinylsulfonate; and mono-ethylenic unsaturated esters of fatty acids (such as vinyl acetate, allyl acetate), monoethylenic unsaturated amides of fatty acids (such as N-vinylacetamide, N-vinylpyrrolidone), ethylenically unsaturated mono-carboxylic acid or dicarboxylic acid esters (such as methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, methyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, benzyl acrylate, 2-ethylhexyl acrylate, cyclohexyl methacrylate, tetrafurfuryl acrylate, isobomyl methacrylate, isobomylacrylate, allylmethacrylate, bisphenol-A dimethacrylate, bromophenyl methacrylate, cyanoethyl methacrylate, glycidyl methacrylate, 1-fluoromethyl methacrylate, 2-fluoroethyl methacrylate, heptadecafluorodecyl methacrylate, heptafluorobutyl methacrylate, hexadecafluorononyl methacrylate, hexafluoro bisphenol-A methacrylate, isocyanatoethyl methacrylate, norbornyl methacrylate, pentachlorophenyl methacrylate, pentaflurobenzyl methacrylate, perfluorooctyl methacrylate, 4-tert-butylcyclohexyl methacrylate, p-tert-butylphenyl methacrylate, trifluroethyl methacrylate, diethyl maleate, diethyl itaconate, ethylenically unsaturated monocarboxylic acid amides (such as acrylamide, dimethyl-acrylamide, methacrylamide, diacetoneacrylamide, acryloyl-morpholine, sodium acrylamide-2-methylpropanesulfonate, methacryloylmorpholine), mono-ethylenically unsaturated compounds (such as acrylonitrile, methacrylonitrile, tetrafluroethylene, vinyl chloride, vinylidene chloride, vinylidene fluoride, vinyl fluoride) and dienes (such as butadiene, isoprene), and in particular, highly hydrophobic compounds are especially preferred among them.
The polymer can be prepared by emulsion polymerization, solution polymerization, suspension polymerization, dispersion polymerization, ionic polymerization (cationic, anionic), Atomic Transfer Radical Polymerization, and other polymerization methods known in the art of polymerization. Most desirable methods are emulsion polymerization and suspension polymerization. If the polymer is prepared by an alternative method, the polymer dispersion can be prepared with a shearing device (such as colloid mill, microfluidizer or other homogenizer) in the presence of gelatin and surfactant.
A water-resistant layer can be formed by fusing the image recording material at a temperature higher than 300xc2x0 F. after the photographic material has been processed to generate an image or the ink-jet image has been formed. The presence of 5-70% by weight of gelatin is sufficient to allow proper permeability for processing solution to diffuse in and out for image development, or for ink to be received by the ink-jet receiving layer. The coating solution is aqueous and can be incorporated in the manufacturing coating operation without any equipment modification. The fusing step is simple and environmentally friendly to photofinishing laboratories.
The image recording elements protected in accordance with this invention can be derived from silver halide photographic elements that can be black and white elements (for example, those which yield a silver image or those which yield a neutral tone image from a mixture of dye forming couplers), single color elements or multicolor elements. Multicolor elements typically contain dye image-forming units sensitive to each of the three primary regions of the spectrum. The imaged elements can be imaged elements which are viewed by transmission, such a negative film images, reversal film images and motion picture prints or they can be imaged elements that are viewed by reflection, such as paper prints. Because of the amount of handling that can occur with paper prints and motion picture prints, they are preferred imaged photographic elements for use in this invention.
The photographic elements in which the images to be protected are formed can have the structures and components shown in Research Disclosure 37038. Specific photographic elements can be those shown on pages 96-98 of Research Disclosure 37038 as Color Paper Elements 1 and 2. A typical multicolor photographic element comprises a support bearing a cyan dye image-forming unit comprised of at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, and a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler. The element can contain additional layers, such as filter layers, interlayers, overcoat layers, subbing layers, and the like. All of these can be coated on a support which can be transparent (for example, a film support) or reflective (for example, a paper support). Support bases that can be used include both transparent bases, such as those prepared from polyethylene terephthalate, polyethylene naphthalate, cellulosics, such as cellulose acetate, cellulose diacetate, cellulose triacetate, and reflective bases such as paper, coated papers, melt-extrusion-coated paper, and laminated papers, such as those described in U.S. Pat. Nos. 5,853,965; 5,866,282; 5,874,205; 5,888,643; 5,888,681; 5,888,683; and 5,888,714. Photographic elements protected in accordance with the present invention may also include a magnetic recording material as described in Research Disclosure, Item 34390, November 1992, or a transparent magnetic recording layer such as a layer containing magnetic particles on the underside of a transparent support as described in U.S. Pat. Nos. 4,279,945 and 4,302,523.
Suitable silver halide emulsions and their preparation, as well as methods of chemical and spectral sensitization, are described in Sections I through V of Research Disclosure 37038. Color materials and development modifiers are described in Sections V through XX of Research Disclosure 37038. Vehicles are described in Section II of Research Disclosure 37038, and various additives such as brighteners, antifoggants, stabilizers, light absorbing and scattering materials, hardeners, coating aids, plasticizers, lubricants and matting agents are described in Sections VI through X and XI through XIV of Research Disclosure 37038. Processing methods and agents are described in Sections XIX and XX of Research Disclosure 37038, and methods of exposure are described in Section XVI of Research Disclosure 37038.
Photographic elements typically provide the silver halide in the form of an emulsion. Photographic emulsions generally include a vehicle for coating the emulsion as a layer of a photographic element. Useful vehicles include both naturally occurring substances such as proteins, protein derivatives, cellulose derivatives (e.g., cellulose esters), gelatin (e.g., alkali-treated gelatin such as cattle bone or hide gelatin, or acid treated gelatin such as pigskin gelatin), gelatin derivatives (e.g., acetylated gelatin, phthalated gelatin, and the like). Also useful as vehicles or vehicle extenders are hydrophilic water-permeable colloids. These include synthetic polymeric peptizers, carriers, and/or binders such as poly(vinyl alcohol), poly(vinyl lactams), acrylamide polymers, polyvinyl acetals, polymers of alkyl and sulfoalkyl acrylates and methacrylates, hydrolyzed polyvinyl acetates, polyamides, polyvinyl pyridine, methacrylamide copolymers, and the like.
Photographic elements can be imagewise exposed using a variety of techniques. Typically exposure is to light in the visible region of the spectrum, and typically is of a live image through a lens. Exposure can also be to a stored image (such as a computer stored image) by means of light emitting devices (such as LEDs, CRTs, etc.).
Images can be developed in photographic elements in any of a number of well known photographic processes utilizing any of a number of well known processing compositions, described, for example, in T. H. James, editor, The Theory of the Photographic Process, 4th Edition, Macmillan, New York, 1977. In the case of processing a color negative element, the element is treated with a color developer (that is one which will form the colored image dyes with the color couplers), and then with an oxidizer and a solvent to remove silver and silver halide. In the case of processing a color reversal element or color paper element, the element is first treated with a black and white developer (that is, a developer which does not form colored dyes with the coupler compounds) followed by a treatment to render developable unexposed silver halide (usually chemical or light fogging), followed by treatment with a color developer. Development is followed by bleach-fixing, to remove silver or silver halide, washing and drying.
Image recording elements in which the images to be protected are formed may also be produced using ink-jet printing. This printing technology is reviewed in an article titled xe2x80x9cProgress and Trends in Ink-Jet Printing Technologyxe2x80x9d by Hue P. Le in the Journal of Imaging Science and Technology, Volume 42, Number 1 (January/February 1998), pp. 49-61. Essentially, ink droplets, typically in the volume range 1-100 picoliters, are ejected from a printhead to a receiver material on which the image is formed. The ink-jet printhead may be of the continuous or drop-on-demand varieties. Several physical mechanisms for drop ejection are known, but the currently most popular among these are thermal and piezoelectric. In the thermal mechanism, ink in the printhead is heated to form a water vapor bubble that expels one or more ink droplets out of the printhead toward the receiver. Representative thermal ink-jet printheads are described in, for example, U.S. Pat. No. 4,723,129 of Endo et al. (Canon) and U.S. Pat. No. 4,490,728 of Vaught et al. (Hewlett Packard). In the piezoelectric mechanism, one or more droplets are expelled from the printhead by a physical deformation that accompanies a voltage change across a piezoelectric material forming a part of the printhead structure. Representative piezoelectric printheads are described in, for example, U.S. Pat. No. 4,459,601 of Howkins (Exxon) and U.S. Pat. No. 5,563,634 of Masahiro et al. (Seiko Epson). Ink-jet inks may be either aqueous- or organic solvent-based. Aqueous inks are preferred for printing in home, office and retail environments. In addition to water and one or more colorants, such as dyes or pigments, an aqueous ink typically contains one or more humectants, which affect ink viscosity and volatility, one or more surfactants, which affect the wetting and penetrating properties of the ink, and a biocide, which extends the useful life of the ink. Aqueous inks may also contain many other ingredients, including metal ion chelating agents, pH buffers, defoamers, and dispersing agents. It is well known to improve the tone scale or bit depth of an image by using more than one ink density for each color. Representative ink-jet inks are described in, for example, U.S. Pat. No. 5,571,850 of Ma et al. (DuPont), U.S. Pat. No. 5,560,770 of Yatake (Seiko Epson), and U.S. Pat. No. 5,738,716 of Santilli et al. (Eastman Kodak). Ink-jet receivers may be reflective, transparent, or of intermediate transparency (e.g., for day/night display materials). At minimum, an ink-jet receiver includes a support and an ink receiving layer. The simplest ink-jet receiver is plain paper, in which these two functions are combined. As a practical matter, more complex receiver structures are required for improved image quality and physical properties. Specifically formulated ink receiving layers coated on paper or other supports improve color density and dot resolution. Receiver composition and structure may also be modified to improve properties such as wettability, ink absorptivity, drying time, gloss, reduced image artifacts, waterfastness, and light and dark stability. Representative ink-jet receiver structures and compositions are described in, for example, U.S. Pat. No. 4,954,395 of Hasegawa et al. (Canon), U.S. Pat. No. 5,725,961 of Ozawa et al. (Seiko Epson), and U.S. Pat. No. 5,605,750 of Romano et al. (Eastman Kodak).
The present invention is illustrated by the following Examples.